December 5, 2007 at 8:47 am
a SAN based HA / DR solution is causing some issues. Let me explain the details.
A SAN technology called 'mirroring' is available to me. it works at the SAN layer where ever bit committed to the disk, gets written twice. Once on the active SAN and once on an offline SAN. The offline SAN is there in the event of primary site hardware failure. The active node is in R/W mode and the passive node is in Read Only mode.
So i boot from local disk where the OS resides. I place the SQL binaries on a local drive. I place all user databases on a SAN device that gets 'mirrored' over to the other datacenter.
everything on paper seems to say this will work.....but;
what if i decide to install SSRS or SSAS???? will the user databases that SSRS creates cause trouble on the passive node when i apply a service pack or hot fix since those databases will be on an offline disk? (SAN Read only mode means the OS does not even see the disk, they are listed as 'offline')
December 5, 2007 at 10:40 am
This is a very deep topic, and one that we almost went with but didn't ($$$). So I've thought about it, but have no practical experience. And so, having presented my credentials...
SSRS will create the two databases (ReportServer, ReportServerTempDB) as normal. If you can't specify where the files are created, you can certainly detach, copy to SAN, and retach them--RS won't care. (I have done this.)
SSAS, I can only assume the same would apply. You specify (or reconfigure from default) where the AS databases reside, and the engine/service won't much care.
In either case, none of this *should* affect the passive SAN node in any way. It doesn't know and could care less what the bytes (let alone files) you're writing are, all it has to do is make sure they get properly written (replicated?) to all configured nodes. Similarly, SQL, RS, and AS shouldn't care where the files are, so long as they can reliably read/write to them.
It seems to me--and here's where my zero experience must be considered--that your real headaches come in when you want to access or otherwise use the files on the passive SAN node. Until then, as you say, it's passive, so no user or application can nohow noway access them--so they're safe. (Or is this how it works? Is it what you want? Are you looking for some kind of read-only mirror of your data?)
So your SAN server dies, and the passive node takes over. How easy is that going to be? Will it work? Is everything configured properly? I can see this being as simple as a normally recovery from an "it broke" situation (which is to say, a royal pain in the :Whistling: ) to as complex as a "now how does this SAN failover stuff really work (while the customers are screaming)" situation. Heh, there's the thing--set it up and test it before you rely on it.
Assuming it works (and I bet you're paying enough that it had better work), simple SAN data replication should be simple, seemless, and foolproof. Accessing and using that data, you'll want to test thoroughly.
Philip
December 5, 2007 at 11:13 am
in the lab i have setup a Metro Mirror on and IBM SAN. failover is not automatic. you have have to 'break' the mirror. Once the mirror is broken, the passive node can 'online' the disks via diskpart.
once the OS sees the disks, i can 'attach' the .MDF's. (the SQL instance is always up since the SQL binaries are on a local disk on both nodes.
again, the concern comes to the ReportServerDB. if I 'move' to the mirrored san, i can just attach when i failover, however, the concern is applying hotfixes and service packs....
SP 1 and SP2 needed ReportServerDB to be online to patch. ( i think :ermm: )
If SSRS was not installed at all, the solution is tested and works. But before I rebuild my lab, i wanted to ask about the ReportServerDB and does it need to be 'online' to be patched.
December 5, 2007 at 8:31 pm
If the upgrade calls for RS to be up and running during the upgrade, then any patches that needed to be made to the DBs themselves will be made to the DBs... and thus, simultaneously, to the mirrored DB files on the passive SAN. If RS is supposed to be offline then, as I can't imagine how the DBs would be upgraded, the DBs would not be upgraded, and once again you're covered.
There might be issues if the server hosting your binaries gets fragged, and you have to reinstall RS on a new server. But if this happens, you'd be best off going through the whole reinstall, DBs and all, so it wouldn't matter which SAN was online.
Leastways, that's how it seems to me.
Philip
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